Expected responses to selection for resistance to the pink stem borer (Sesamia calamistis Hampson) and the sugarcane borer (Eldana saccharina Walker) in two maize populations

Progenies from two maize populations, one white-grained (DMR ESR-W) and the other yellow (DMR ESR-Y) were evaluated under artificial infestation with two borer species (Sesamia calamistis and Eldana saccharina) in two seasons to predict responses and correlated responses to selection for resistance to stem borers. Correlations between grain yield and most agronomic parameters were significant. There were negative correlations between grain yield and damage parameters in both maize populations. The highest genotypic correlation coefficient was observed between grain yield and stem tunneling (rg = -0.52) in DMR ESR-Y, and with stalk breakage (rg = -0.67) in DMR ESR-W. A Rank Summation Index (RSI) generated using plant aspect, grain yield, stem tunneling, leaf feed¬ing and tolerance had positive phenotypic correlations with damage parameters, but negative relationship with agronomic traits. All agronomic parameters including grain yield will increase with selection. Grain yield increase of about 210 kg/ha will be obtained per generation in DMR ESR-W using two seasons to complete a cycle, but a relatively low increase (73 kg ha-1) is expected in DMR ESR-Y. Response from single trait selection was better than from RSI in DMR ESR-Y, but reverse was the case in DMR ESR-W. Correlated responses to selection showed that direct selection for most of the traits would be better than indirect selection through any other trait. Appreciable progress is expected from selection for improvement of the maize populations for resistance to the two borer spe¬cies, although progress from selection may be slow

Natural convection in asymmetric triangular enclosures heated from below

Triangular enclosures are typical configurations of attic spaces found in residential as well as industrial pitched-roof buildings. Natural convection in triangular rooftops has received considerable attention over the years, mainly on right-angled and isosceles enclosures. In this paper, a finite volume CFD package is employed to study the laminar air flow and temperature distribution in asymmetric rooftop-shaped triangular enclosures when heated isothermally from the base wall, for aspect ratios (AR) 0.2 64 AR 64 1.0, and Rayleigh number (Ra) values 8 7 105 64 Ra 64 5 7 107. The effects of Rayleigh number and pitch angle on the flow structure and temperature distributions within the enclosure are analysed. Results indicate that, at low pitch angle, the heat transfer between the cold inclined and the hot base walls is very high, resulting in a multi-cellular flow structure. As the pitch angle increases, however, the number of cells reduces, and the total heat transfer rate progressively reduces, even if the Rayleigh number, being based on the enclosure height, rapidly increases. Physical reasons for the above effect are inspected

Variability for resistance to the pink stem borer (Sesamia calamistis Hampson) and the sugarcane borer (Eldana saccharina Walker) in two tropical maize populations

A set of 100 S1 plants were selected from a white and yellow maize population to generate both full-sib and half-sib progenies using North Carolina Design II (NCD II) mating scheme. The 250 progenies generated in each population were evaluated under artificial infestation with two borer species (Sesamia calamistis and Eldana saccharina) at two locations in two seasons to determine levels of genetic variability for improvement purposes. There were wide ranges for most of the traits studied in both maize populations. Plant height and grain yield were significantly reduced with mean grain yield loss being between 25 and 30%. In the white population, additive variance was larger than dominance variance for grain yield, days to 50% silking, stalk breakage and ear per plant, but for the yellow counterpart, additive variance was larger for plant height, ear per plant, leaf feeding and cob damage. None of the gene actions was important for dead heart. Narrow-sense heritability was low to moderate for the resistance parameters. It ranged from 1.45% for leaf feeding to 40.6% for stalk breakage in the white population, and from 3.80% for leaf feeding to 40.1% for cob damage in the yellow population. Heritability for grain yield was 37.6% in the white population but much lower (10.5%) in the yellow population. Although, heritability was low to moderate for the traits studied, the wide ranges and moderate additive variances obtained suggest that substantial genetic variability exist in the two maize populations for reasonable improvement to be made. Breeding scheme that capitalizes on both additive and dominance gene action would be effective for improving the populations for stem borer resistance and grain yield

Modelling of Heat Transfer Through Hollow Blocks Produced with Rice-Husk-Ash Blended Cement.

Hollow sandcrete blocks are widely used in many countries of the world. In recent years, cement content is being partially substituted by admixtures especially agricultural wastes. Modeling of heat transfer characteristics of these modified blocks is essential in order to predict their thermal performance. This study focuses on this modeling with the aid of a finite-volume based computer code. Specifically, for regular, two-cavity blocks produced with the cement partially substituted with rice husk ash (RHA). The result showed that as the percentage substitution of RHA increased, thermal gradient across the width of the block increased, while the rate of heat flow reduced. The second part of the study examined the effect of heat transfer through the air-gap as compared to a similar study regarding it as vacuum. The heat flow through the air-gaps of the building bricks affected the pattern of heat flow within the bricks, hence, they could not be regarded as a vacuum. The results of this study will be useful to building professionals in the choice of building blocks and proper estimation of air- conditioning load in buildings

A Critical Review of Buoyancy-induced Flow Transitions in Horizontal Annuli

The main mechanisms of transition of buoyancy-induced flows in the horizontal annulus betweencircular cylinders are reviewed, based on the available literature. Both experimental and theoreticalstudies are considered. The different scenarios for the evolution of the flow regimes and temperaturepatterns are tracked, for increasing values of the Rayleigh number, Ra. The occurrence of variousinstability and bifurcative phenomena is pointed out, and linked to other relevant parameters, such asthe radius ratio R and the Prandtl number, Pr. Although most of the relevant literature is on 2D cases, theeffect of the third dimension is considered as far as possible. Studies on the influence of the eccentricityof the inner cylinder on the laminar flow and the thermal asset are also reviewed. Finally, open questionsand topics for future research are hinted at

A Comprehensive Review of Natural Convection in Triangular Enclosures

Natural convection in triangular enclosures is an important problem. It displays well the generic attributes of this class of convection, with its dependence on enclosure geometry, orientation and thermal boundary conditions. It is particularly rich in its variety of flow regimes and thermal fields as well as having significant practical application. In this paper, a comprehensive view of the research area is sought by critically examining the experimental and numerical approaches adopted in studies of this problem in the literature. Different thermal boundary conditions for the evolution of the flow regimes and thermal fields are considered. Effects of changes in pitch angle and the Rayleigh number on the flow and thermal fields are examined in detail. Although most of the past studies are in the laminar regime, the review extends up to the recent studies of the low turbulent regime. Finally, areas of further research are highlighted